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Just wanted to chime in here for a bit. I was talking with John some, and as one of the people out there that has really spent a lot of time trying things and fiddling with the JandS and as an electrical control systems engineer as my "day job" I wanted to bring my comments and perspective.

I have a Mazda MP3 boosting about 13 psi right now (due to wastegate issues) that is making a bit over 260 whp. I run a Microtech standalone system and the JandS Safeguard for my engine control electronics.

First of all... for the gentleman refering to the use of a knock window as being "not ideal" I have to ask how it is anything less than ideal? Yielding a specific TDC marker point yields no feasible gain. Ideal peak cylinder pressure is typically stated as needing to occur around 14 degrees ATDC for maximum power output. While this will vary to some degree due to how well it is being targeted by the tuner as well as by variations in mechanical aspects of the motor (but only marginally.. it is still commonly accepted that regardless of engine construction 14 degreest ATDC is ideal for peak cylinder pressure). The reason I bring this point up is that peak cylinder pressure is typically the most conducive to detonation. Additionally, any case where the flame front slams into the piston due to overly aggressive timing would typically occur within a few degrees of this location unless timing is so severely over advanced that most generalized scenarios are no longer applicable. Thus using the JandS scenario for the window locations of peak pressure are straddled appropriate and the range where piston rock is occuring (at top dead center) that can lead to false triggers in most systems, is avoided. Detonation is much more an effect of timing than of strict reference to TDC, and thus by using the window that John is using, you are much more relative to the appropriate measurement of location for this phenomenon. Additionally, in conversations I've had with John, he has indicated that it would be possible to move the window per request... have fun gettign any other manufacturer to adjust the software in their units for you.

Now moving on to the headphone users... I've personally built a couple units myself for use with noise canceling head phones and have added various levels of filtering and so forth. Simply put, the JandS id'ed and corrected detonation well before it was ever to a point of being audible and distinguishable to my ears. In other words, it was typically much higher level detonation. Keep in mind that by the time most detonation is audible a considerable amount of high level detonation has already taken place. Apparently John's algorithm is sensitive enough to detect it based on my experience. For those that will immediately jump on me to cry wolf that the JandS was false triggering... an adjustment of 3-4 degrees of timing on my EMS eliminated all triggers from the JandS and when added back in yielded the same response from the JandS. Again there was no hope or prayer of hearing this detonation through the head phones by any stretch. I tried quite a bit and ran numerous experiments to see if I could hear the detonation. So again, while headphones may work great (and do!) for hearing detonation in some cases, the underlying fact is there is considerable detonation occuring at high levels that are inaudible amidst the engine noise that the JandS is identifying successfully.

I'm sure there will be more to respond to when some of you read through and counterpoint to my statements. I'm happy to hear alternative points of view, but wanted to express some of my opinions on the matter (and no I do not profit from, sell, or carry any sponsorship or association with JandS... just am an avid user with experience that has shown me the value in the system).

I've been thinking about making a product like this that incorporates a FM modulator so you can just listen through your car stereo / or FM headphones. I'm curious how much interest there would be. You could also do some cool stuff interfacing to a PC via the sound card input and using FFTs and normalization to a recovered tach signal to see the knock events in time / energy plots referenced to TDC...

I've been thinking about making a product like this that incorporates a FM modulator so you can just listen through your car stereo / or FM headphones. I'm curious how much interest there would be. You could also do some cool stuff interfacing to a PC via the sound card input and using FFTs and normalization to a recovered tach signal to see the knock events in time / energy plots referenced to TDC...

Knock sensors are just a form of microphone, so I see no reason you couldn't hook it directly up to your car's stereo with the right adaptor. You might need to use a pre-amp of some sort if the noise floor on your stereo isn't very low, or if the signal is very weak.

As for the normalization and such, most modern ECUs already do all that. They have a "knock window" referenced to TDC as well as a specific set of frequencies. Good ECUs will have a RPM/Load "noise" map, which amounts to a normalization map, though it doesn't continuously renormalize; it's just set once at the factory.

I've been thinking about making a product like this that incorporates a FM modulator so you can just listen through your car stereo / or FM headphones. I'm curious how much interest there would be. You could also do some cool stuff interfacing to a PC via the sound card input and using FFTs and normalization to a recovered tach signal to see the knock events in time / energy plots referenced to TDC...

I have used both FM modulators and wired adapters with my TXS TunerPRO. The FM modulators pick up on electrical noise in the car and you hear that noise as det. Once I switched to a wired adapter that "noise DET" was gone. There was one other guy around here that ran into the same problem. I would stick with a wired adapter unless you want to chase random "noise DET".

I have used both FM modulators and wired adapters with my TXS TunerPRO. The FM modulators pick up on electrical noise in the car and you hear that noise as det. Once I switched to a wired adapter that "noise DET" was gone. There was one other guy around here that ran into the same problem. I would stick with a wired adapter unless you want to chase random "noise DET".

TMS

Good point. The idea behind using the FM modulator was to simplify the installation for people utilize their existing stereo. Sound like from your experience that is too much of a comprimise. It would still be interesting to see how well a PC could analyze the knock sensor signal to detect really low level knocking using some decent signal processing techniques.

It would still be interesting to see how well a PC could analyze the knock sensor signal to detect really low level knocking using some decent signal processing techniques.

It's not at all clear (to me, at least) that any PC can provide a realtime answer to the knock question. However, it seems very clear that a PC could be programmed to analyze (post process) a knock sensor's output and decide whether or not knock was present.

I don't know if this is what you were thinking, but, though I've never really used it like this, I've experimented with hooking one of those cassete shaped thingies (what folks use to play their MP3 players through their car stereo) into my TUNA.

Seemed to work just fine, but I prefer putting headphones on (when I'm tuning in the passenger seat, of course.)

I have a post somewhere on here about hooking up a knock sensor to your PC and using simple (usually free) sound processing software to filter out other engine noise. The valves in my engine tap at about the same frequency as knock, but you can still hear it.

I just bought a Bosch knock sensor at the junkyard and wired it to a mini-audio jack (radio shack has one's that come with alligator clips), and plugged it into my computer. Set the filtering software to "play through," filtered out all sound except 5-10 kHz, and it worked great. You can either play it through head phones or right out of the speakers of the computer.

The valve noise is atrocious--one person told me it's the buckets rattling on top of the valves that are making all that racket.

The valve noise is atrocious--one person told me it's the buckets rattling on top of the valves that are making all that racket.

Hence, the concept of a "knock window" where you only listen during the period when knock is likely to occur, which happens to coincide with a period when the valves aren't closing (at least on 4-cylinder engines). According to p. 9 of http://focus.ti.com/lit/an/spra039/spra039.pdf:

Quote:

Detection Strategies
Knock detection strategies use the output of a signal conditioning stage to compare with a reference to determine the presence or absence of knock. Most systems today use windowing to isolate periods during the cylinder’s firing cycle for analysis when knock is possible. There is a window from approximately 10° to 70° after top dead center (ATDC) of the piston’s cycle when detonation is most likely to occur for the firing cylinder. The detection algorithm is run only during this window for that cylinder. By eliminating possible false trigger sources, such as valve closing, the detection algorithm is more robust. The time this window is active varies with engine speed from 20 ms at 500 RPM down to 1.25 ms at 8000 RPM. Tracking changing engine speed to calculate this time variation requires hardware or software overhead for implementation.

That TI document, BTW, is a very good introduction to knock detection.

BTW, I've read at least one Subaru patent that adjusts the knock window based on IAM (e.g. if IAM is low, the knock window is shifted farther from TDC).

The J&S Safeguard system tries to employ a "knock window" but, unfortunately is unable to identify TDC or crank angle degrees ATDC. Their "window" is described in a post at http://www.eng-tips.com/viewthread.cfm?qid=54276 but it doesn't necessarily exclude valve closing noise:

Quote:

Hi to all. My name is John Pizzuto, and I'm the designer of the J&S SafeGuard.

In the mid '90's, a GM engineer sent me a list of GM sensors, showing part numbers, resonant frequencies, parrallel load resistance, and mounting style.

At the time, they were producing sensors in these frequencies: 5.2kHz, 6.0kHz, and 7.0kHz.

A chart from the SAE paper shows that the fundamental frequency of a 75mm bore is about 7kHz, a 94mm bore is about 6.0 kHz, while that of a 110mm bore is about 5.2kHz. The chart shows a fairly linear relationship of frequency to bore diameter.

The paper terms the GM sensors to be "broadband resonant", with "bandwidths approaching one thoundsand hertz".

The detector in the J&S unit is in software, running on a 68HC11. The unit controls dwell and timing as well.

Software sets up a knock window, since knock is expected to occur around TDC. The window opens 32° after the ignition trigger, and remains open for 44°.

A load qualifier is used to disable the detector under light engine loads and decel, where piston slap can cause a large interfering signal.

The unit uses a proprietary algorithm to develop a threshold, against which the signal is compared.

The classic knock detection method is emodied in the TI chip TPIC8101 - Knock Signal Interface. It is a reincarnation of the Harris HIP9010 chip (do a search, it's no longer available). I've seen a Subaru patent that essentially implements this processing in the digital domain.

And then there's the idea that you can discern knock by its "signitaure" instead of its relative loudness. That idea is espoused by http://researchnews.osu.edu/archive/knock.htm and you can see its embodiment here:
where the "backslash" lines represent knock and its declining frequency.

I think you could design a meter that eliminates almost all the valve noise if you could isolate the frequencies.

Interesting web site. I agree that knock has a certain change in pitch that makes it distinct from all other noise, hence even if you are hearing the valves click away, knock sticks out. The human ear is great at detecting the change in pitch (frequency). I'm sure you could get a computer to do it, but it won't be easy.

A PC can do it in realtime, there was a guy who made his own filter in LabView for his Porshe tuning days.

So far I've used a stock knock (not the stock one, another stock one) sensor spliced into a headphone jack and pluged into an amp (laptop) and then plugged into headphones for listening. I use a set of Bose noise canceling headphones (QC2s and yay for employee discount otherwise I wouldn't have them). So far so good and soon I'll have the TXS Tuner at my door. The bonus of the raw audio is you can record it with a laptop and use the spectrograph as shown above. That works well but I've found our engines to be VERY noisy with the spectrograph and you have to mess with it to clean it up. I have had more luck just listening than trying to analyse.